ABSTRACT: Tumor cell invasion and metastasis are hallmarks of malignancy. Despite recent advances in the understanding of lymphatic spread, the mechanisms by which tumors metastasize to sentinel/distant lymph nodes and beyond are poorly understood. To gain new insights into this complex process, we established a highly metastatic melanoma cell line (B16F1-variant) by in vivo passaging the B16 parental cell line through the lymphatic system. Here, we characterized morphology, rate of cell proliferation, colony formation, migration, tumorogenicity, lymph flow, and capacities to induce tumor- and sentinel lymph node- lymphangiogenesis. Furthermore, microarray-based comparative analysis bewteen parental and passaged cell lines was performed to identify specific gene expression profiles. The most differentially expressed gene was SPP (osteopontin), a secreted glycophosphoprotein which is known to be involved in cancer metastasis. Overexpression of osteopontin in B16 F1-variant was confirmed by Western blot and quantitative RT-PCR. Treatment of cultured lymphatic endothelial cells (LEC) with osteopontin promoted cell migration mediated by the integrin α9 pathway. Our results identify osteopontin as a novel lymphangiogenic factor. B16 and B16 variants were cultured in DMEM supplemented with 20% fetal bovine serum (FBS; Invitrogen, Grand Island, NY) supplemented with antibiotic-antimycotic solution. Every B16 variant was cultured in duplicates. Total cellular RNA was isolated using the Trizol reagent (Invitrogen, Carlsbad, CA) extracted with chloroform, precipitated with isopropanol, washed with 70% ethanol, and dissolved in DNase-free/RNase-free distilled water. The concentration of RNA was measured using NanoDrop ND-1000 spectrophotometer (Witec AG, Littau, Switzerland) and RNA quality was assessed using 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA). Digoxigenin-UTP–labeled cRNA was generated and amplified from 500ng of total RNA using the NanoAmp RT-IVT Labeling Kit (Applied Biosystems, Foster City, CA) following the manufacturer's protocol, and was hybridized to Applied Biosystems Mouse Genome Survey Microarrays V2.0. Chemiluminescence detection, image acquisition, and analysis were performed using the Chemiluminescence Detection Kit (Applied Biosystems) and the Applied Biosystems 1700 Chemiluminescent Microarray Analyzer following the manufacturer's protocol. A total of two biological replicates were generated for each B16 variant and each cell line data consisted of pooled RNA of two diffferent passage numbers.
